Fluid knives, particularly air knives, air showers and the like are in common use in many different environments. For example, when air is used for treatment purposes at a high velocity in a controlled manner, an air knife becomes very helpful. For example, in carpet manufacture, air is used in dewatering as well as to blow gently across the tufting to cause the fiber to stand upright.
In the papermaking field an air knife becomes extremely useful particularly in regard to the wet end of a papermaking machine such as for purposes of a sheet knock-off. Also, at the dry end of the papermaking process, an air knife is adaptable for use in felt cleaning and drying as well as in coating procedures.
The one difficulty existing with air knife structures has been in the area of orifice adjustment. Generally they utilize a structure such as a large bolt every foot or so to force open or close two angle pieces. This type of arrangement is not adaptable for a uniform orifice sizing or for close control over orifice adjustment particularly at different points along the length of an extended orifice arrangement.
Examples of prior art in this area are present in U.S. Pat. Nos. 1,759,804 and 3,977,359 where the art of deckling is utilized to control the length of orifice openings.
Furthermore, U.S. Pat. No. 3,977,359 goes into greater detail as to the advantages of having a greater air flow at the ends than at the center when blowing hot metal, such as zinc, off a sheet or strip of base metal. In this teaching, the concept is accomplished by using adjustable air jets internally to control air flows. Other references of interest include U.S. Pat. No. 1,625,472 directed to a pulp web cutter; U.S. Pat. No. 2,610,555 directed to a pair of bar cutters for welting at right angles and U.S. Pat. No. 3,841,910 a general teaching of a method and apparatus for extracting from traveling porous webs.
In general, the background shows that air knifes are used in a variety of different environments for different purposes. However, it is also apparent that there are considerable limitations as to the control over orifice openings particularly with respect to the concept and flexibility of orifice adjustment and variability of orifice openings over an elongated slot or aperture.